My vote goes to story B.
Story A:
This one was solid. I don't like the whole concept of a Venus colony, and I think the overwhelming heat should have a little more emphasis in the story. For example, Pietro gets out of the shower, presumably barefoot, so shouldn't his feet be burning? Do they have heat-resistant flip flops too? Overall, I think that the prose was pretty good, although there were some awkward sentences, like "A short glass syringe, tucked away inside a foam padding in a box under Pietro’s bed" could be condensed to "A short glass syringe, tucked away inside a foam padded box underneath the bed". Also, two people have relations together, not relationships. In the end, I noticed most of the required elements, but there's no sentient planet (although it would've been really sick if it was implied that Venus is alive), treehugger, or humanitarian. Also, it's debatable if the fungus is psionic weaponry or not. Some fanfare is deserved, however, because it's a complete entry that fulfills almost all of the requirements.
Story B:
I enjoyed this story, although naming the two characters Carl and Carlos is atrocious for reading comprehension. You do differentiate them via dialogue--a good detail which I actually enjoyed--but it still fucking hurts my head, especially because it was completely unnecessary. This story jumps right in, showing us an unforgiving alien planet (giving me some Deathworld vibes) that requires the Helldivers laser cannon, and colonists at odds with their government. Then, we get the zealot, alongside the psionic weaponry (which is also the fungus, cool!). It's terrifying that the fungus gives people future sight and backflip powers; thankfully, the main characters have a laser cannon! Oh wait, it's forgotten about after it's used on the village and the fungus. This story also had some typos and awkward phrases, such as "With all the vindictive rage in his heart, he swung the sword down heavily on the crown of the cultist's head, feeling it crack and smash". The second clause is oddly phrased to my mind, and a head shouldn't be cracked and smashed by a sword, but rather chopped. Weird imagery. Otherwise, I did enjoy the majority of the prose, and I think it contains the most necessary elements (missing only humanitarian and unethical scientist by my interpretation). Fanfare might be warranted for the best story of the three.
Story C:
Story C falls into the pitfall of telling, not showing. We get a paragraph of exposition (in the form of summarizing this planet [not sentinet either]), followed by more paragraphs of exposition (in the form of summarizing characters that we don't even meet), followed by a brief dialogue that leads into a vague summary of a conversation (instead of the actual conversation, which the readers don't know the contents of). Then, we finally arrive at the meat of the story: something crazy is going down, and our character is caught right in the middle. Now, he has to help his brother solve this civil war... wait, you summarized that part too?! I was finally enticed by something in the story, and it just ends. There's plenty of the necessary elements included, but the story doesn 't hold up unfortunately.
This story really needed to put those additional 1132 words to use, but at least it got submitted, I guess. World's smallest violin can be the fanfare here.
Overall, I enjoyed the first two stories, but B develops faster, is a little more dynamic, and containins a few more of the required motifs, so I think it comes out on top. C is begging to be rewritten, because the idea could definitely go places with more development.